Five ml heparinized whole blood was drawn for QFT-G before for PPD testing. The blood specimens were incubated for 16-20 h (overnight) at 37°C in a humidified atmosphere. IFN-γ levels in the nil well were considered background and were subtracted from the results of the mitogen well and the antigen-stimulated wells. The results were considered positive if the concentration of. IFN-γ in the sample well after stimulation with ESAT-6 and/or CFP-10 was greater than or equal to 0.35 IU/ml (after subtracting the value of the nil well), regardless of the results of the positive control (mitogen well). The results were considered negative if the response to the specific antigens (after subtracting the value of the nil well) was less than 0.35 IU/ml and if the IFN-γ levels of the positive control (after subtracting the value of the nil well) were greater than or equal to 0.5 IU/ml. The results were considered indeterminate if both antigen-stimulated sample wells were negative (i.e., <0.35 IU/ml after subtracting the value of the Nil well) and if the value of the positive control well was less than 0.5 IU/ml after subtracting the value of